1. Field of the Invention
The invention relates to an imaging device, and particularly to an imaging device that simultaneously obtains a plurality of angles of view such as a wide angle image and a telescopic image.
2. Description of the Related Art
Zoom functions in an image input device such as a video camera, a digital camera or a monitoring camera have been widely used these days, by which a change of the focal distance of a lens or scale-up or scale-down of an image is easily performed, according to a distance to or a size of an angle of view toward an object to be shot. The zoom functions can be classified into an optical zoom function and an electronic zoom function. The optical zoom function can be realized by mechanically moving a lens inside. On the other hand, the electronic zoom function may make use of part of an image output from an imager to generate an image by complementing a new pixel among pixels and magnify it. The electronic zoom function has an advantage that it may be realized as compact without a driving portion and at a low cost, compared with the optical zoom function. However, it has a problem that it is inferior in image quality.
In order to solve the problem, there is proposed an electronic zoom image input system as shown in FIG. 14, which includes an image input optical unit with a fixed focal distance for compressing a circumferential part of an input image, a photo detector with a uniform density of pixels for receiving the image through the system, and a unit for complementing and correcting the image received by the photo detector having distortion caused by the compression. The image input system is characteristic of obtaining a zoomed image of an equivalent resolution in the operating region. See, for example, Japanese Patent Publication Hei 10-233950. The system is expected to produce an image having less deterioration in the middle of both a wide angle image and a telescopic image, regardless of unavoidable deterioration in a peripheral part thereof.
The image input system of the prior art described above has a structure as shown in FIG. 16, in which a zoom center position of a lens agrees with a center position of an imager. The zoom center position is defined by a position in which the lens can form the most magnified optical image. Under the situation, the optical image incident on the photo detector, as shown in FIG. 17, the central portion is expanded and the circumferential portion is compressed. As a result of this, since the image contains more pixel information in the central portion, image processing can produce a fine, zoomed image for the central portion. By contrast, because the image has less pixel information in the circumferential portion, a fine, zoomed image therefore cannot be obtained. This is a problem.
Under the situation, when there is no object in the middle, the prior art described above, as shown in FIG. 15, discloses that two cuneate prism lenses are inserted, each being rotated independently.